This invention relates to catalytic dewaxing hydrocarbon feed materials. More particularly, this invention relates to a single-step catalytic dewaxing process for production of lube oil base stocks from a wide range of feeds including relatively low quality, contaminant-containing, waxy hydrocarbon feeds, fuel oils, waxy lube oil distillates, waxy lube oil solvent raffinates, lube oil distillates, and raffinates which have previously been partially dewaxed by solvent dewaxing.
Catalytic dewaxing of petroleum and synthetic crude oil fractions in the presence of shape-selective catalysts capable of selectively cracking n-paraffins and isoparaffins is well-known. For example, U.S. Pat. No. Re. 28,398 (Chen et al.), which is a reissue of U.S. Pat. No. 3,700,585, discloses the use of shape-selective crystalline aluminosilicate zeolite ZSM-5 in catalytic dewaxing processes directed at removing high freezing point paraffins from jet fuel to lower the freezing point, improving the octane rating of naphtha fractions and lowering the pour point of lube oil base stocks. According to Chen et al., the shape selective cracking ability of crystalline aluminosilicate ZSM-5 permits selective cracking of n-paraffins and certain isoparaffins without substantial cracking of desirable feed components such that improved catalytic dewaxing products are obtained under both hydrotreating and hydrocracking conditions. Chen et al. also disclose the use of crystalline aluminosilicate zeolite ZSM-5 associated with hydrogenating metals such as tungsten, vanadium, molybdenum, rhenium, nickel, cobalt, chromium, manganese, platinum or palladium, such metals being associated with the zeolite by exchange or impregnation.
U.S. Pat. No. Re. 30,529, which is a reissue of U.S. Pat. No. 4,100,056, discloses catalytic dewaxing of atmospheric and vacuum distillates in the presence of a catalyst containing mordenite in hydrogen form and a Group VI or VIII metal to obtain naphthenic lube oils of intermediate viscosity index and pour points ranging from -50.degree. to +20.degree. F.
U.S. Pat. No. 4,222,855 (Pelrine et al.) discloses catalytic dewaxing of 450.degree.-1,050.degree. F. hydrocarbon fractions to produce high viscosity index lube oils employing a catalyst containing crystalline aluminosilicate zeolite ZSM-23 or ZSM-35, preferably in hydrogen form and associated with platinum, palladium or zinc. According to the abstract, the use of catalysts containing crystalline aluminosilicate zeolite ZSM-23 or ZSM-35 gives products of higher viscosity index and lower pour point than products obtained through the use of crystalline aluminosilicate zeolite ZSM-5.
U.S. Pat. No. 4,247,388 (Banta et al.) is directed to improving crystalline aluminosilicate zeolites such as ZSM-5 in terms of dewaxing performance by treatment to adjust alpha activity. According to the patentee, alpha activity is adjusted by partial replacement of cationic sites of the crystalline aluminosilicate zeolite with basic cations such as sodium, by partial coking of the zeolite, by employing the zeolite in combination with an inert matrix material, by manipulating the silica-to-alumina ratio of the zeolite or, preferably, by steaming. Crystalline aluminosilicate zeolites adjusted in terms of alpha activity can be employed in association with exchanged or impregnated hydrogenating metals such as tungsten, vanadium, molybdenum, rhenium, nickel, cobalt, chromium, manganese, platinum or palladium. A disclosure similar to that of Banta et al. is found in an abstract of British Pat. No. 2,027,742.
U.S. Pat. No. 4,251,348 and U.S. Pat. No. 4,282,085 (both O'Rear) are directed to processes similar to those described hereinabove wherein a low nitrogen content petroleum distillate fraction boiling from 180.degree.-1,200.degree. F. is contacted with crystalline aluminosilicate zeolite ZSM-5 or a similar crystalline aluminosilicate zeolite in a form substantially lacking in hydrogenation activity to form an effluent which then is fractionated into an upgraded product stream and a C.sub.3 -C.sub.4 olefin fraction. If desired, the crystalline aluminosilicate zeolite can be dispersed in a porous matrix having only insubstantial cracking activity. Suitable matrix materials include pumice, firebrick, diatomaceous earth, alumina, silica, zirconia, titania, amorphous silica-alumina mixtures, bentonite, kaolin, silica-magnesia, silica-zirconia or silica-titania. A similar disclosure is found in an abstract of Belgium Pat. No. 877,772.
U.S. Pat. No. 4,259,174 (Chen et al.) discloses catalytic dewaxing of hydrocarbon feeds to reduce pour point and produce high viscosity index distillate lube oil stocks in the presence of a synthetic offretite crystalline aluminosilicate zeolite catalyst which may contain exchanged or impregnated hydrogenating metals such as tungsten, vanadium, molybdenum, rhenium, nickel, cobalt, chromium, manganese, platinum or palladium. The crystalline aluminosilicate zeolite may be dispersed within a matrix of alumina, silica, silica-alumina, etc. (Column 5, line 67-Column 6, line 17). It is unclear whether the patentee contemplates use of the crystalline aluminosilicate zeolite in association with both hydrogenating metals and matrix materials.
An abstract of British Pat. No. 2,055,120 (Mobil) discloses a method for reclaiming or upgrading contaminated, dewaxed lube oil base stocks having a tendency to form a waxy haze during storage, comprising contacting the oil with hydrogen at 500.degree.-675.degree. F. and a space velocity of 2-10 in the presence of a crystalline aluminosilicate zeolite having a silica-to-alumina ratio of at least 12 and a constraint index of 1-12.
Another catalytic dewaxing process is disclosed in U.S. Pat. No. 4,360,419 (Miller). In particular, a hydrocarbonaceous feed containing normal and slightly-branched chain hydrocarbons is contacted with a catalyst which comprises a hydrogenation component and a zeolite having a mole ratio of an oxide selected from silicon oxide, germanium oxide, and mixtures thereof to an oxide selected from aluminum oxide, gallium oxide, and mixtures thereof greater than about 5:1 and having X-ray diffraction lines as shown in the '419 specification.
U.S. Pat. No. 4,343,692 (Winquist) discloses a process for catalytically hyrodewaxing distillates or residual fractions by contacting the same with hydrogen and a catalyst comprising a synthetic ferrierite zeolite having incorporated therewith at least one metal selected from the group consisting of Group VIB, Group VIIB and Group VIII.
U.S. Pat. No. 4,388,177 (Bowes et al.) discloses a process for selectively hydrocracking straight chain and single-methyl branched hydrocarbons contained in a reformate or waxy hydrocarbon oil feed by contacting the feed with hydrogen and a catalyst composition comprising a natural ferrierite and at least one hydrogenation component selected from the metals of Group VIA and Group VIII. The natural ferrierite is pretreated by contacting it with an oxalate ion under conditions effective to impart to the ferrierite a constraint index from about 1 to 12.
Yet another dewaxing process is disclosed in U.S. Pat. No. 4,390,414 (Cody) which process involves contacting a waxy hydrocarbon oil stock in the presence of hydrogen with a zeolite which has been chemically modified by reaction, under dry, anhydrous conditions, with an organosilane wherein the zeolite has some sites capable of reacting with the organosilane and wherein said organosilane is: (a) capable of entering into the channels of the zeolite and chemically reacting with the reactive sites present therein, as well as (b) capable of reacting with hydroxyl groups present on the external surface of said zeolite, and which zeolite has been loaded with a catalytically active hydrogenating metal component, the contacting being conducted under conditions of pressure, temperature and liquid flow velocity sufficient to effect the hydrodewaxing. The zeolite contemplated for use in the Cody reference is any natural or synthetic unfaulted aluminosilicate material.
Another relevant disclosure is found in U.S. Pat. No. 4,176,050 (Chen et al.) directed to a dewaxing process using macrocrystalline ZSM-5 preferably associated with a hydrogenation metal such as platinum, palladium, zinc, or nickel.
U.S. Pat. No. 4,153,540 (Gorring et al.) teaches a process for upgrading shale oil with a dewaxing catalyst comprising a metal such as nickel or palladium together with a crystalline zeolite having a silica to alumina ratio greater than 12 and a constraint index of 1 to 12, such as ZSM-5.
Along the same vein, U.S. Pat. No. 3,968,024 (Gorring et al.) discloses a dewaxing process using a catalyst comprising crystalline aluminosilicate zeolite such as ZSM-5 together with a metal selected from the group consisting of zinc, cadmium, palladium, and nickel.
As can be gleaned from the above, the art is replete with various catalytic dewaxing processes wherein the catalyst employed typically contains an aluminosilicate.
A further relevant disclosure is found in U.S. Pat. No. 4,431,518 (Angevine et al.) wherein a process for the reduction of the pour point of an oil feedstock is disclosed utilizing a catalyst comprising a boron-containing material having an X-ray diffraction pattern substantially as set out in the subject patent. The X-ray diffraction pattern shown in the subject patent is that of a conventional aluminosilicate zeolite ZSM-5. The patentee points out that a borosilicate-containing dewaxing catalyst is superior to the conventional aluminosilicate containing dewaxing catalysts discussed above because the borosilicate-containing dewaxing catalyst is substantially more nitrogen resistant and thus can be used to dewax feedstocks containing high concentrations of nitrogen compounds. The subject patent is silent with respect to the efficacy afforded by a catalyst containing a Group VIII noble metal and a borosilicate material in connection with a dewaxing process. The subject patent further broadly teaches the cation-exchange of the original alkali metal of the boron-containing zeolite ZSM-5 with cations selected from the group consisting of metal ions, ammonium ions, and hydrogen ions, where metal ions include those selected from the group consisting of metals of Groups II and VIII of the periodic table, rare earth metals, calcium and manganese.
In preparation of lube oils from hydrocarbon feeds, catalytic dewaxing processes such as described hereinabove often are combined with hydrotreating, hydrocracking and/or various solvent extraction steps to obtain products having desired properties. Typically, hydrocracking and/or solvent extraction steps are conducted prior to catalytic dewaxing to remove components such as metal-containing feed components, asphaltenes and polycyclic aromatics having properties that differ grossly from those desired. In particular, solvent extraction is conducted to remove polycyclic aromatic feed components and nitrogen-containing cyclic components, removal of the latter being particularly important in order to avoid poisoning of the catalyst in catalytic dewaxing. Hydrotreating under mild or severe conditions typically follows catalytic dewaxing operations and serves to improve such lube oil properties as stability and viscosity index.
One example of a process for producing lube oils in which a catalytic dewaxing step is included as part of a multistep process, namely U.S. Pat. No. 4,259,170 (Graham et al.), discloses a process that includes a combination of catalytic dewaxing and solvent dewaxing steps. According to a more specific aspect of Graham et al., the process includes a solvent extraction step prior to the dewaxing steps. As a further example of a multistep process for preparation of lube oils, Chen et al. '714, discussed hereinabove, discloses a process comprising solvent extraction followed by catalytic dewaxing.
U.S. Pat. No. 4,283,272 (Garwood et al.) discloses preparation of lube oils by a process that includes hydrocracking, catalytic dewaxing and hydrotreating steps.
U.S. Pat. No. 4,292,166 (Gorring et al.) discloses a combination process wherein a dewaxing step is carried out prior to a hydrocracking step. Specifically, a hydrocarbon oil feed selected from the group consisting of vacuum gas oils, deasphalted oils and mixtures thereof is converted to a low pour point, high VI lube base stock by first dewaxing the feed in the presence of hydrogen and a dewaxing catalyst comprising a zeolite having a constraint index of 1 to 12, followed by contacting the dewaxed feedstock and hydrogen with a hydroconversion catalyst comprising a platinum group metal and a zeolite having a silica-to-alumina ratio of at least 6.
Finally, a combination process is disclosed in European Patent Application No. 82300226.6 (Smith et al.) wherein a hydrocarbon oil containing impurities deleterious to the catalyst is first treated with a sorbent comprising a first molecular sieve zeolite having pores with an effective diameter of at least about 5 Angstroms under sorption conditions, followed by a treatment with a dewaxing catalyst comprising a second molecular sieve zeolite having pores with an effective diameter of at least about 5 Angstroms, the effective diameter of which is equal to or smaller than the effective diameter of the pores of the first molecular sieve zeolite. In a more specific aspect of the disclosure, the first and second molecular sieves have the same crystal structure wherein the constraint index is 1 to 12 and the dried hydrogen-form crystal density is less than about 1.6 grams per cubic centimeter.
Despite the plethora of catalytic dewaxing processes disclosed in the art there is still a need for an improved catalytic dewaxing process. More specifically, there is a need for a catalytic dewaxing process wherein the dewaxing catalyst is nitrogen-resistant and produces a lube base product possessing an improved VI coupled with greater lube base stock yields.
Accordingly, it is an object of the present invention to provide a process for dewaxing feedstocks which contain nitrogen compounds which process produces lube base stocks in higher yields possessing greater VIs.
It has now been discovered that a particular molecular sieve-containing catalyst produces improved results in connection with a hydrocarbon dewaxing process. In particular, a dewaxing process employing a catalyst comprising a crystalline borosilicate and a Group VIII noble metal component results in high lube yields with concomitantly less light gas make. Further, the process of the present invention provides a lube oil base stock possessing a high viscosity index and a reduced sulfur content. The combination of above benefits is achieved when the dewaxing process is carried out in accordance with the present invention.
In connection with the present invention it should be noted that hydrogen processing catalysts containing an AMS-type borosilicate molecular sieve coupled with catalytic metal components are known. For instance, commonly assigned U.S. Pat. No. 4,434,047 (Hensley, Jr. et al.) discloses a catalytic dewaxing hydrotreating process using a catalyst containing a shape-selective zeolitic cracking component such as an AMS-type borosilicate molecular sieve, and a hydrogenating component containing Cr, at least one other Group VIB metal and at least one Group VIII metal. U.S. Pat. No. 4,268,420 similarly discloses an AMS-type crystalline borosilicate which can be used in intimate combination with a hydrogenating component, such as tungsten, vanadium, molybdenum, rhenium, nickel, cobalt, chromium, manganese, or a noble metal, such as platinum or palladium, or rare earth metals, where a hydrogenation-dehydrogenation function is to be performed.
Further, co-pending commonly assigned U.S. Ser. No. 200,536 discloses catalytic compositions comprising chromium, molybdenum, at least one Group VIII metal, a crystalline molecular sieve, and a refractory inorganic oxide, suitable for use in a process for hydrogenation and hydrocracking of high-nitrogen content feeds. The subject application also discloses the use of a crystalline borosilicate in connection with the above-described catalytic composition.